Minimizing buffer requirements in a digital video system

ABSTRACT

According to some embodiments of the invention, a method of minimizing buffer requirements, in a packet based multimedia system having a multimedia source device coupled to a multimedia display device by way of a bi-directional auxiliary channel arranged to transfer information between the display device and the source device and vice versa and a unidirectional main link arranged to carry multimedia data packets from the multimedia source device to the multimedia display device is disclosed. Interspersing special characters that allow the display device to distinguish each bit of pixel data included in the data packets thereby requiring only a small FIFO type buffer unit.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application takes priority under 35 U.S.C. 119(e) to (i)U.S. Provisional Patent Application No.: 60/467,804, filed on May 1,2003 entitled “DIGITAL/ANALOG VIDEO INTERCONNECT AND METHODS OF USETHEREOF” by Kobayashi, (ii) U.S. Provisional Patent Application No.:60/504,060 filed on Sep. 18, 2003, entitled “DIGITAL/ANALOG VIDEOINTERCONNECT AND METHODS OF USE THEREOF” by Kobayashi, (iii) U.S.Provisional Patent Application No.: 60/474,085filed on May 28, 2003,entitled “DIGITAL/ANALOG VIDEO INTERCONNECT AND METHODS OF USE THEREOF”by Kobayashi, and (iv) U.S. Provisional Patent Application No.:60/474,084 filed on May 28, 2003, entitled “SIMPLE ENUMERATION METHODFOR THE LINK CLOCK RATE AND THE PIXEL/AUDIO CLOCK RATE” by Kobayashieach of which are hereby incorporated by reference herein in theirentirety. This application is also related to the following co-pendingU.S. Patent applications, which are filed concurrently with thisapplication and each of which are herein incorporated by reference, (i)U.S. patent application Ser. No. 10/726,802 , entitled “METHOD OFADAPTIVELY CONNECTING A VIDEO SOURCE AND A VIDEO DISPLAY” namingKobayashi as inventor; (ii) U.S. patent application Ser. No. 10/726,438,entitled “METHOD AND APPARATUS FOR EFFICIENT TRANSMISSION OF MULTIMEDIADATA PACKETS” naming Kobayashi as inventor; (iii) U.S. patentapplication Ser. No. 10/726,794, entitled “PACKET BASED VIDEO DISPLAYINTERFACE AND METHODS OF USE THEREOF”, naming Kobayashi as inventor;(iv) U.S. patent application Ser. No. 10/726,440, entitled “PACKET BASEDMONITOR TRAINING IN A VIDEO SYSTEM”, naming Kobayashi as inventor; (v)U.S. patent application Ser. No. 10/726,350, entitled “TECHNIQUES FORREDUCING MULTIMEDIA DATA PACKET OVERHEAD”, naming Kobayashi as inventor;(vi) U.S. patent application Ser. No. 10/726,362, entitled “PACKET BASEDCLOSED LOOP VIDEO DISPLAY INTERFACE WITH PERIODIC STATUS CHECKS”, namingKobayashi as inventor; (vii) U.S. patent application Ser. No.10/726,441, entitled “VIDEO INTERFACE ARRANGED TO PROVIDE PIXEL DATAINDEPENDENT OF A LINK CHARACTER CLOCK”, naming Kobayashi as inventor.This application is also related to the following co-pendingapplications: (viii) U.S. patent application Ser. No. 10/909,103,entitled “USING PACKET TRANSFER FOR DRIVING LCD PANEL DRIVERELECTRONICS” filed July 29, 2004, naming Kobayashi as inventor; and (ix)U.S. patent application Ser. No. 10/909,085, entitled “PACKET BASEDSTREAM TRANSPORT SCHEDULER AND METHODS OF USE THEREOF” filed Jul. 29,2004, naming Kobayashi as inventor.

FIELD OF THE INVENTION

The invention relates to display devices. More specifically, theinvention relates to digital display interface suitable for couplingvideo sources to video display devices.

BACKGROUND OF THE INVENTION

Currently, video display technology is divided into analog type displaydevices (such as cathode ray tubes) and digital type display devices(such as liquid crystal display, or LCD, plasma screens, etc.), each ofwhich must be driven by specific input signals in order to successfullydisplay an image. For example, a typical analog system includes ananalog source (such as a personal computer, DVD player, etc.) coupleddirectly to a display device (sometimes referred to as a video sink) byway of a communication link. The communication link typically takes theform of a cable (such as an analog VGA cable in the case of a PC,otherwise referred to as VGA DB15 cable) well known to those of skill inthe art. For example, the VGA DB15 cable includes 15 pins, each of whichis arranged to carry a specific signal.

One of the advantages of the VGA DB15 cable is the ubiquitous nature ofthe cable, due to the large and ever-expanding installed base. As longas the analog systems described above predominate, there is littleincentive to migrate away from any other cable form than the VGA DB15.

However, in recent years, the exploding growth of digital systems hasmade the use of digital capable cables such as Digital Visual Interface(DVI) cable more desirable. It is well known that DVI is a digitalinterface standard created by the Digital Display Working Group (DDWG).Data are transmitted using the transition minimized differentialsignaling (TMDS) protocol, providing a digital signal from the PC'sgraphics subsystem to the display. DVI handles bandwidths in excess of160 MHz and thus supports UXGA and HDTV with a single set of links.

Today's display interconnect landscape includes the VGA (analog) and DVI(digital) for desktop display interconnect applications as well as LVDS(digital) for internal connectivity applications within laptops andother all-in-one devices. Graphics IC vendors, display controller ICvendors, monitor manufacturers and PC OEMs as well as desktop PCconsumers, to one degree or another, must factor interface choice intotheir design, product definition, manufacturing, marketing and purchasedecisions. For example, if a consumer purchases a PC with an analog VGAinterface then the consumer must either purchase an analog monitor or adigital monitor in which the analog video signal provided by the VGAinterface has been digitized by way of an inline analog to digitalconverter (ADC) or an ADC built into the particular monitor.

Therefore, it would be desirable to have a digital interface that ismore efficient in allocating buffer space.

SUMMARY OF THE INVENTION

According to some embodiments of the invention, a method of minimizingbuffer requirements, in a packet based multimedia system having amultimedia source device coupled to a multimedia display device by wayof a bi-directional auxiliary channel arranged to transfer informationbetween the display device and the source device and vice versa and aunidirectional main link arranged to carry multimedia data packets fromthe multimedia source device to the multimedia display device isdisclosed. The method can be carried out by following at least theoperations of communicating via the auxiliary channel data packetattributes to the display device prior to commencement of transmissionof the data packets from the source device to the display device overthe main link, forming a reduced size data packet header for each of thedata packets wherein the reduced size is commensurate with the datapacket attributes already communicated via the auxiliary channel,associating the reduced size data packet header with a corresponding oneof the data packets, transmitting the data packet and associated reducedsize data packet header from the source device to the display deviceover the main link, and interspersing special characters that allow thedisplay device to distinguish each bit of pixel data included in thedata packets thereby requiring only a small FIFO type buffer unit.

In another embodiment, an apparatus for minimizing buffer requirement ina packet based multimedia system having a multimedia source devicecoupled to a multimedia display device by way of a bi-directionalauxiliary channel arranged to transfer information between the displaydevice and the source device and vice versa and a unidirectional mainlink arranged to carry multimedia data packets from the multimediasource device to the multimedia display device is disclosed. Theapparatus includes at least means for communicating via the auxiliarychannel data packet attributes to the display device prior tocommencement of transmission of the data packets from the source deviceto the display device over the main link, means for forming a reducedsize data packet header for each of the data packets wherein the reducedsize is commensurate with the data packet attributes alreadycommunicated via the auxiliary channel, means for associating thereduced size data packet header with a corresponding one of the datapackets, and means for transmitting the data packet and associatedreduced size data packet header from the source device to the displaydevice over the main link and interspersing special characters thatallow the display device to distinguish each bit of pixel data includedin the data packets thereby requiring only a small FIFO type bufferunit.

In still another embodiment, computer program product for minimizingbuffer requirement in a packet based multimedia system having amultimedia source device coupled to a multimedia display device by wayof a bidirectional auxiliary channel arranged to transfer informationbetween the display device and the source device and vice versa and aunidirectional main link arranged to carry multimedia data packets fromthe multimedia source device to the multimedia display device. Thecomputer program product includes computer code for communicating viathe auxiliary channel data packet attributes to the display device priorto commencement of transmission of the data packets from the sourcedevice to the display device over the main link, computer code forforming a reduced size data packet header for each of the data packetswherein the reduced size is commensurate with the data packet attributesalready communicated via the auxiliary channel, computer code forassociating the reduced size data packet header with a corresponding oneof the data packets, computer code for transmitting the data packet andassociated reduced size data packet header from the source device to thedisplay device over the main link and computer code for interspersingspecial characters that allow the display device to distinguish each bitof pixel data included in the data packets thereby requiring only asmall FIFO type buffer unit and computer readable medium for storing thecomputer code.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a generalized representation of a cross platform displayinterface 100 in accordance with an embodiment of the invention.

FIGS. 2A-2C illustrates a video interface system that is used to connecta video source and a video display unit in accordance with a number ofembodiments of the invention.

FIG. 3 shows exemplary main link rates in accordance with an embodimentof the invention.

FIG. 4A shows a main link data packet in accordance with an embodimentof the invention.

FIG. 4B shows a main link packet header in accordance with an embodimentof the invention.

FIG. 5A shows a system arranged to provide sub-packet enclosure andmultiple-packet multiplexing in accordance with an embodiment of theinvention.

FIG. 5B shows another implementation of the system shown in FIG. 5A.

FIG. 6 shows a high-level diagram of the multiplexed main link stream asan example of the stream shown in FIG. 5.

FIG. 7 show another example of a data stream in accordance with theinvention.

FIG. 8 shows yet another example of a multiplexed data stream inaccordance with an embodiment of the invention.

FIG. 9A shows a representative sub-packet in accordance with anembodiment of the invention.

FIG. 9B shows a representative main link data packet in accordance withan embodiment of the invention.

FIG. 10 shows an example of a selectively refreshed graphics image.

FIG. 11 shows an exemplary link training pattern in accordance with anembodiment of the invention.

FIG. 12 illustrates a logical layering of the system in accordance withan embodiment of the invention.

FIG. 13 shows an exemplary special character mapping using 8B/10B inaccordance with an embodiment of the invention.

FIG. 14 shows an exemplary Manchester II encoding scheme in accordancewith an embodiment of the invention.

FIG. 15 shows a representative auxiliary channel electrical sub layer inaccordance with an embodiment of the invention.

FIG. 16 shows a representative main link electrical sub layer inaccordance with an embodiment of the invention.

FIG. 17 shows a representative connector in accordance with anembodiment of the invention.

FIG. 18 shows a source state diagram in accordance with an embodiment ofthe invention.

FIG. 19 shows a display state diagram in accordance with an embodimentof the invention.

FIGS. 20-24 illustrate various computer based implementations of theinvention.

FIG. 25 shows a flowchart detailing a process for determining anoperational mode of the interface in accordance with an embodiment ofthe invention.

FIG. 26 shows a flowchart detailing a process for providing a real timevideo image quality check in accordance with some aspects of theinvention.

FIG. 27 a shows a flowchart for a first part of a link set up process inaccordance with an embodiment of the invention.

FIG. 27 b shows a flowchart for a second part of a link set up processin accordance with an embodiment of the invention.

FIG. 28 shows a flowchart detailing a process for performing a trainingsession in accordance with an embodiment of the invention.

FIG. 29 illustrates a computer system employed to implement theinvention.

DETAILED DESCRIPTION OF SELECTED EMBODIMENTS

Reference will now be made in detail to a particular embodiment of theinvention an example of which is illustrated in the accompanyingdrawings. While the invention will be described in conjunction with theparticular embodiment, it will be understood that it is not intended tolimit the invention to the described embodiment. To the contrary, it isintended to cover alternatives, modifications, and equivalents as may beincluded within the spirit and scope of the invention as defined by theappended claims.

The inventive interface is a point-to-point, packet-based, plug & play,serial digital display interface that is both open and scalable that issuitable for use with, but not limited to, desktop monitors as well asproviding LCD connectivity within notebook/all-in-one PC's, and consumerelectronics display devices including HDTV displays and the like. Unlikeconventional display interfaces that transmit a single video raster plustiming signals such as Vsync, Hsync, DE, etc., the inventive interfaceprovides a system of multi-stream packet transfer capable oftransferring one or more packet streams simultaneously in the form of“virtual pipes” established within a physical link.

For example, FIG. 1 shows a generalized representation of a crossplatform packet based digital video display interface 100 in accordancewith an embodiment of the invention. The interface 100 connects atransmitter 102 to a receiver 104 by way of a physical link 106 (alsoreferred to as a pipe). In the described embodiment, a number of datastreams 108-112 are received at the transmitter 102 that, if necessary,packetizes each into a corresponding number of data packets 114. Thesedata packets are then formed into corresponding data streams each ofwhich are passed by way of an associated virtual pipe 116-120 to thereceiver 104. It should be noted that the link rate (i.e., the datapacket transfer rate) for each virtual link can be optimized for theparticular data stream resulting in the physical link 106 carrying datastreams each having an associated link rate (each of which could bedifferent from each other depending upon the particular data stream).The data streams 110-114 can take any number of forms such as video,graphic, audio, etc.

Typically, when the source is a video source, the data streams 110-114include various video signals that can have any number and type ofwell-known formats, such as composite video, serial digital, paralleldigital, RGB, or consumer digital video. The video signal can be ananalog video signal provided the source 102 includes some form of ananalog video source such as for example, an analog television, stillcamera, analog VCR, DVD player, camcorder, laser disk player, TV tuner,set top box (with satellite DSS or cable signal) and the like. Thesource 102 can also include a digital image source such as for example adigital television (DTV), digital still camera, and the like. Thedigital video signal can be any number and type of well known digitalformats such as, SMPTE 274M-1995 (1920×1080 resolution, progressive orinterlaced scan), SMPTE 296M-1997 (1280×720 resolution, progressivescan), as well as standard 480 progressive scan video.

In the case where the source 102 provides an analog image signal, ananalog-to-digital converter (A/D) converts an analog voltage or currentsignal into a discrete series of digitally encoded numbers (signal)forming in the process an appropriate digital image data word suitablefor digital processing. Any of a wide variety of A/D converters can beused. By way of example, other A/D converters include, for example thosemanufactured by: Philips, Texas Instrument, Analog Devices, Brooktree,and others.

For example, if the data stream 110 is an analog type signal, the ananalog to digital converter (not shown) included in or coupled to thetransmitter 102 will digitize the analog data which is then packetize bya packetizer that converts the digitized data stream 110 into a numberof data packets 114 each of which will be transmitted to the receiver104 by way of the virtual link 116. The receiver 104 will thenreconstitute the data stream 110 by appropriately recombining the datapackets 114 into their original format. It should be noted that the linkrate is independent of the native stream rates. The only requirement isthat the link bandwidth of the physical link 106 be higher than theaggregate bandwidth of data stream(s) to be transmitted. In thedescribed embodiment, the incoming data (such as pixel data in the caseof video data) is packed over the respective virtual link based upon adata mapping definition. In this way, the physical link 106 (or any ofthe constituent virtual links) does not, as does conventionalinterconnects such as DVI, carry one pixel data per link characterclock.

In this way, the interface 100 provides a scaleable medium for thetransport of not only video and graphics data, but also audio and otherapplication data as may be required. In addition, the invention supportshot-plug event detection and automatically sets the physical link (orpipe) to its optimum transmission rate. The invention provides for a lowpin count, purely digital display interconnect for all displays suitablefor multiple platforms. Such platforms include host to display,laptop/all-in-one as well as HDTV and other consumer electronicsapplications.

In addition to providing video and graphics data, display timinginformation can be embedded in the digital stream providing essentiallyperfect and instant display alignment, obviating the need for featureslike “Auto-Adjust” and the like. The packet based nature of theinventive interface provides scalability to support multiple, digitaldata streams such as multiple video/graphics streams and audio streamsfor multimedia applications. In addition, a universal serial bus (USB)transport for peripheral attachment and display control can be providedwithout the need for additional cabling.

Other embodiments of the inventive display interface will be discussedbelow.

FIG. 2 illustrates a system 200 based upon the system 100 shown in FIG.1 that is used to connect a video source 202 and a video display unit204. In the illustrated embodiment, the video source 202 can includeeither or both a digital image (or digital video source) 206 and ananalog image (or analog video source) 208. In the case of the digitalimage source 206, a digital data stream 210 is provided to thetransmitter 102 whereas in the case of the analog video source 208, anA/D converter unit 212 coupled thereto, converts an analog data stream213 to a corresponding digital data stream 214. The digital data stream214 is then processed in much the same manner as the digital data stream210 by the transmitter 102. The display unit 204 can be an analog typedisplay or a digital type display or in some cases can process eitheranalog or digital signals provided thereto. In any case, the displayunit 204 includes a display interface 216 that interfaces the receiver104 with a display 218 and a D/A converter unit 220 in the case of ananalog type display. In the described embodiment, the video source 202can take any number of forms (such as a personal desktop computer,digital or analog TV, set top box, etc.) whereas the video display unit104 can take the form of a video display (such as an LCD type display,CRT type display, etc.).

Regardless of the type of video source or video sink, however, thevarious data streams are digitized (if necessary) and packetized priorto transmission over the physical link 106 which includes auni-directional main link 222 for isochronous data streams and abi-directional auxiliary channel 224 for link setup and other datatraffic (such as various link management information, Universal serialbus (USB) data, etc.) between the video source 202 and the video display204.

The main link 222 is thereby capable of simultaneously transmittingmultiple isochronous data streams (such as multiple video/graphicsstreams and multi-channel audio streams). In the described embodiment,the main link 222 includes a number of different virtual channels, eachcapable of transferring isochronous data streams (such as uncompressedgraphics/video and audio data) at multiple gigabits per second (Gbps).From a logical viewpoint, therefore, the main link 222 appears as asingle physical pipe and within this single physical pipe, multiplevirtual pipes can be established. In this way, logical data streams arenot assigned to physical channels rather, each logical data stream iscarried in its own logical pipe (i.e., virtual channel described above).

In the described embodiment, the speed, or transfer rate, of the mainlink 222 is adjustable to compensate for link conditions. For example,in one implementation, the speed of the main link 222 can be adjusted ina range approximated by a slowest speed of about 1.0 Gbps to about 2.5Gbps per channel in approximately 0.4 Gbps increments (see FIG. 3). At2.5 Gbps per channel, the main link 222 can support SXGA 60 Hz with acolor depth of 18 bits per pixel over a single channel. It should benoted that a reduction in the number of channels reduces not only thecost of interconnect, but also reduces the power consumption which is animportant consideration (and desirable) for power sensitive applicationssuch as portable devices and the like. However, by increasing the numberof channels to four, the main link 222 can support WQSXGA (3200×2048image resolution) with a color depth of 24-bits per pixel at 60 Hz. orQSXGA (2560×2048) with a color depth of 18-bits per pixel at 60 Hz,without data compression. Even at the lowest rate of 1.0 Gbps perchannel, only two channels are required to support an uncompressed HDTV(i.e., 1080i or 720p) data stream.

In the described embodiment, a main link data rate is chosen whosebandwidth exceeds the aggregate bandwidth of the constituent virtuallinks. Data sent to the interface arrives at the transmitter at itsnative rate. A time-base recovery (TBR) unit 226 within the receiver 104regenerates the stream's original native rate using time stamps embeddedin the main link data packets, if necessary. It should be noted,however, that for appropriately configured digital display devices 232shown in FIG. 2B, time base recovery is unnecessary since display datais be sent to the display driver electronics at the link character clockrate, thereby greatly reducing the number of channels required with acommensurate reduction in complexity and cost for the display. Forexample, FIG. 2C illustrates an exemplary LCD panel 232 configured insuch a way that no time base recovery since display data is essentiallypipelined to the various column drivers 234 that are used in combinationwith row drivers 236 to drive selected display elements 238 in the array240.

Other embodiments describe a simple enumeration method for the link rateand the pixel/audio clock rate. It has been researched and understoodthat all the standard pixel/audio clock frequencies that exist today area subset of the following master frequency:23.76 GHz=210×33×57×111 HzThis means that a pixel (or audio) clock rate can be expressed with fourparameters, A, B, C, and D as:Pixel clock rate=2A*3B×5C×11D

-   -   A=4 bits, B=2 bits, C=3 bits, and D=1 bit.

Even for a link whose link rate (which is the serial link bit rate/10for a link that uses 10-bit character such as 8B/10B characters) may bedifferent from the pixel clock rate, there is a benefit in defining thelink rate with these four parameters, A′, B′, C′, and D′: The benefit isthe simplicity in regenerating pixel/audio clocks from a link clock. Forexample, let's say the link rate is set as A′=6, B′=3, C′=7, and D′=0and the corresponding link rate is 135 MHz. However, suppose the pixelclock rate is set as A=8, B=3, C=6, and D=0 (=108 MHz), then the pixelclock can be generated from link clock as pixel clock rate is equal tothe link rate*22/5 1.

Referring back to those systems requiring time base recovery, thetime-base recovery unit 226 may be implemented as a digital clocksynthesizer. For an uncompressed video stream, the time stamp is storedin the packet header which as described in more detail below, is a20-bit value. For a given stream, four of 20 bits are stored in eachheader successively (TS3-0, TS7-4, TS11-8, TS15-12, TS19-16). Nativestream frequency (Freq_native) is obtained from link character clockfrequency (Freq_link_char) as:Freq_native=Freq_link_char*(TS19-0)/220  Eq(1)

The transmitter 102 generates this time stamp by counting the number ofnative stream clocks in 220 cycles of the link character clock frequencyperiod. The counter updates the value every 220 cycles of the linkcharacter clock. Since these two clocks are asynchronous with eachother, the time stamp value will change by 1 over time. Between updates,the transmitter 102 will repeatedly send the same time stamp in theheader of the given packet stream. A sudden change of the time stampvalue (by more than 1 count) may be interpreted by the receiver as anindication of an unstable condition of the stream source.

It should be noted that, no time stamp is communicated for an audiostream. In this case, the source device informs the display device ofthe audio sample rate and number of bits per sample. By determining theaudio rate based upon Eq(2) and the link character rate, the displaydevice regenerates the original audio stream rate.Audio rate=(audio sample rate)×(# bits per sample)×(# channels)  Eq(2)

A main link data packet 400 shown in FIG. 4A includes a main link packetheader 402 as shown in FIG. 4B that is formed of 16 bits where bits 3-0are the Stream ID (SID) (indicating that maximum stream count is 16),bit 4 is the Time Stamp (TS) LSB. When bit 4 is equal to 1, this packetheader has the least significant 4 bits of Time Stamp value (used onlyfor uncompressed video stream). Bit 5 is a Video frame sequence bitwhich acts as the least significant bit of the frame counter whichtoggles from “0” to “1” or from “1” to “0” at the video frame boundary(used only for uncompressed video stream). Bits 7 and 6 are reservedwhereas bits 8 through 10 are a 4-bit CRC (CRC) that checks errors forthe previous eight bits. Bits 15-12 are Time Stamp/Stream ID Inversion.(TSP/SIDn) which for uncompressed video are used as four bits of 20-bitTime Stamp value.

One of the advantages of the inventive interface is the ability tomultiplex different data streams each of which can be different formatsas well as have certain main link data packets include a number of subpackets. For example, FIG. 5 shows a system 500 arranged to providesub-packet enclosure and multiple-packet multiplexing in accordance withan embodiment of the invention. It should be noted that the system 500is a particular embodiment of the system 200 shown in FIG. 2 and shouldtherefore not be construed as limiting either the scope or intent of theinvention. The system 500 includes a stream source multiplexer 502included in the transmitter 102 used to combine a stream 1 supplementaldata stream 504 with the data stream 210 to form a multiplexed datastream 506. The multiplexed data stream 506 is then forwarded to a linklayer multiplexer 508 that combines any of a number of data streams toform a multiplexed main link stream 510 formed of a number of datapackets 512 some of which may include any of a number of sub packets 514enclosed therein. A link layer de-multiplexer 516 splits the multiplexeddata stream 510 into its constituent data streams based on the streamIDs (SIDs) and associated sub packet headers while a stream sinkde-multiplexer 518 further splits off the stream 1 supplemental datastream contained in the sub-packets.

FIG. 6 shows a high-level diagram of the multiplexed main link stream600 as an example of the stream 510 shown in FIG. 5 when three streamsare multiplexed over the main link 222. The three streams in thisexample are: UXGA graphics (Stream ID=1), 1280×720p video (Stream ID=2),and audio (Stream ID=3). The small packet header size of main linkpacket 400 minimizes the packet overhead, which results in the very highlink efficiency. The reason the packet header can be so small is thatthe packet attributes are communicated via the auxiliary channel 224prior to the transmission of the packets over main link 222.

Generally speaking, the sub-packet enclosure is an effective scheme whenthe main packet stream is an uncompressed video since an uncompressedvideo data stream has data idle periods corresponding to thevideo-blanking period. Therefore, main link traffic formed of anuncompressed video stream will include series of Null special characterpackets during this period. By capitalizing on the ability to multiplexvarious data streams, certain implementations of the present inventionuse various methods to compensate for differences between the main linkrate and the pixel data rate when the source stream is a video datastream. For example, as illustrated in FIG. 7, the pixel data rate is0.5 Gb/sec, such that a bit of pixel data is transmitted every 2 ns. Inthis example, the link rate has been set to 1.25 Gb/sec, such that a bitof pixel data is transmitted each 0.8 ns. Here, transmitter 102intersperses special characters between pixel data as illustrated inFIG. 8. Two special characters are disposed between a first bit of pixeldata P1 and a second bit of pixel data P2. The special characters allowreceiver 104 to distinguish each bit of pixel data. Interspersing thespecial characters between bits of pixel data also creates a steadystream of data that allows the link to maintain synchronization. In thisexample, the special characters are Null characters. No line buffer isneeded for such methods, only a small FIFO, because the link rate issufficiently fast. However, relatively more logic is required on thereceiving side to reconstruct the video signal. The receiver needs torecognize when the special characters begin and end.

An alternative to the interspersing method is to alternate consecutivebits of pixel data with special characters, such as null values. Forexample, P1 through P4 could be fed into a line buffer included in thetransmitter 104, then one or more null values could be fed into thebuffer until more pixel data are available. Such implementations requirea relatively larger buffer space than the interspersing methodsdescribed above. In many such implementations, the time required to fillthe line buffer will exceed the time required to transmit the data afterthe line buffer is full, due to the relatively high link speeds.

As discussed with reference to FIG. 5A, one of the advantages of theinventive interface is the ability to not only multiplex various datastreams, but also the enclosing of any of a number of sub packets withina particular main link data packet. FIG. 9A shows a representativesub-packet 900 in accordance with an embodiment of the invention. Thesub-packet 900 includes a sub-packet header 902 that in the describedembodiment is 2 bytes and is accompanied by SPS (Sub-Packet Start)special character. If the main link data packet in which the sub-packet900 is enclosed contains a packet payload in addition to the sub-packet900, the end of the sub-packet 900 must be marked by SPE (Sub-PacketEnd) special character. Otherwise, the end of the main packet (asindicated by ensuing COM character in the example shown in FIG. 9B)marks the end of both the sub-packet 902 and the main packet into whichit is enclosed. However, a sub-packet does not need to end with SPE whenits enclosing main packet has no payload. FIG. 9B shows an exemplarysub-packet format within a main link packet in accordance with anembodiment of the invention. It should be noted that the definition ofthe header field and sub-packet payload is dependent on the specificapplication profile that uses the sub-packet 902.

A particularly useful example of sub-packet enclosure usage is selectiverefresh of an uncompressed graphics image 1000 illustrated in FIG. 10.The attributes of the entire frame 1002 (Horizontal/Vertical Total,Image Width/Height, etc.) will be communicated via the auxiliary channel224 since those attributes stay constant as long as the stream remainsvalid. In selective refresh operation, only a portion 1004 of the image1000 is updated per video frame. The four X-Y coordinates of the updatedrectangle(s) (i.e., the portion 1004) must be transmitted every framesince the values of the rectangle coordinates changes from frame toframe. Another example is the transmission of color look-up table (CLUT)data for required for 256-color graphic data where the 8-bit pixel datais an entry to the 256-entry CLUT and the content of the CLUT must bedynamically updated.

The single bi-directional auxiliary channel 224 provides a conduit tofor various support functions useful for link set up and supporting mainlink operations as well as to carry auxiliary application data such asUSB traffic. For example, with the auxiliary channel 224, a displaydevice can inform the source device of events such as sync loss, droppedpackets and the results of training sessions (described below). Forexample, if a particular training session fails, the transmitter 102adjusts the main link rate based upon pre-selected or determined resultsof the failed training session. In this way, the closed loop created bycombining an adjustable, high speed main link with a relatively slow andvery reliable auxiliary channel allows for robust operation over avariety of link conditions. It should be noted that in some cases (anexample of which is shown in FIG. 5B), a logical bi-directionalauxiliary channel 520 can be established using a portion 522 of thebandwidth of the main link 222 to transfer data from the source device202 to the sink device 204 and a uni-directional back channel 524 fromthe sink device 204 to the source device 202. In some applications, useof this logical bi-directional auxiliary channel may be more desirablethan using a half-duplex bi-directional channel described in FIG. 5A.

Prior to starting the transmission of actual packet data streams thetransmitter 102 establishes a stable link through a link trainingsession that is analogous in concept to the link setup of the modem.During link training, the main link transmitter 102 sends a pre-definedtraining pattern so that the receiver 104 can determine whether it canachieve a solid bit/character lock. In the described embodiment,training related handshaking between the transmitter 102 and thereceiver 104 is carried on the auxiliary channel. An example of a linktraining pattern is shown in FIG. 11 in accordance with an embodiment ofthe invention. As illustrated, during the training session, a phase 1represents the shortest run length while phase 2 is the longest that areused by the receiver to optimize an equalizer. In phase 3, both bit lockand character lock are achieved as long as the link quality isreasonable. Typically, the training period is about 10 ms, in whichtime, approximately 107 bits of data are sent. If the receiver 104 doesnot achieve solid lock, it informs the transmitter 102 via the auxiliarychannel 224 and the transmitter 102 reduces the link rate and repeatsthe training session.

In addition to providing a training session conduit, the auxiliarychannel 224 can be also used to carry main link packet streamdescriptions thereby greatly reducing the overhead of packettransmissions on the main link 222. Furthermore, the auxiliary channel224 can be configured to carry Extended Display Identification Data(EDID) information replacing the Display Data Channel (DDC) found on allmonitors (EDID is a VESA standard data format that contains basicinformation about a monitor and its capabilities, including vendorinformation, maximum image size, color characteristics, factory pre-settimings, frequency range limits, and character strings for the monitorname and serial number. The information is stored in the display and isused to communicate with the system through the DDC which sites betweenthe monitor and the PC graphics adapter. The system uses thisinformation for configuration purposes, so the monitor and system canwork together). In what is referred to as an extended protocol mode, theauxiliary channel can carry both asynchronous and isochronous packets asrequired to support additional data types such as keyboard, mouse andmicrophone.

FIG. 12 illustrates a logical layering 1200 of the system 200 inaccordance with an embodiment of the invention. It should be noted thatwhile the exact implementation may vary depending upon application,generally, a source (such as the video source 202) is formed of a sourcephysical layer 1202 that includes transmitter hardware, a source linklayer 1204 that includes multiplexing hardware and state machine (orfirmware), and a data stream source 1206 such as Audio/Visual/Graphicshardware and associated software. Similarly, a display device includes aphysical layer 1208 (including various receiver hardware), a sink linklayer 1210 that includes de-multiplexing hardware and state machine (orfirmware) and a stream sink 1212 that includes display/timing controllerhardware and optional firmware. A source application profile layer 1214defines the format with which the source communicates with the linklayer 1204 and similarly, a sink application profile layer 1216 definesthe format with which the sink 1212 communicates with the sink linklayer 1210.

The various layers will now be discussed in more detail.

Source Device Physical Layer

In the described embodiment, the source device physical layer 1202includes an electrical sub layer 1202-1 and a logical sub layer 1202-2.The electrical sub layer 1202-1 includes all circuitry for interfaceinitialization/operation such as hot plug/unplug detection circuit,drivers/receivers/termination resistors,parallel-to-serial/serial-to-parallel conversions, andspread-spectrum-capable PLL's. The logical sub layer 1202-2 includescircuitry for, packetizing/de-packetizing, datascrambling/de-scrambling, pattern generation for link training,time-base recovery circuits, and data encoding/decoding such as 8B/10B(as specified in ANSI X3.230-1994, clause 11) that provides 256 linkdata characters and twelve control characters (an example of which isshown as FIG. 13) for the main link 222 and Manchester II for theauxiliary channel 224 (see FIG. 14).

It should be noted that the 8B/10B encoding algorithm is described, forexample, in U.S. Pat. No. 4,486,739, which is hereby incorporated byreference. As known by those of skill in the art, the 8B/10B code is ablock code that encodes 8-bit data blocks into 10-bit code words forserial transmission. In addition, the 8B/10B transmission code convertsa byte wide data stream of random 1s and 0s into a DC balanced stream of1s and 0s with a maximum run length of 5. Such codes provide sufficientsignal transitions to enable reliable clock recovery by a receiver, suchas transceiver 110. Moreover, a DC balanced data stream proves to beadvantageous for fiber optic and electromagnetic wire connections. Theaverage number of 1s and 0s in the serial stream is be maintained atequal or nearly equal levels. The 8B/10B transmission code constrainsthe disparity between the number of 1 s and 0s to be −2, 0, or 2 across6 and 4 bit block boundaries. The coding scheme also implementsadditional codes for signaling, called command codes.

It should be noted that in order to avoid the repetitive bit patternsexhibited by uncompressed display data (and hence, to reduce EMI), datatransmitted over main link 222 is first scrambled before 8B/10Bencoding. All data except training packets and special characters willbe scrambled. The scrambling function is implemented with LinearFeedback Shift Registers (LFSRs). When data encryption is enabled, theinitial value of an LFSR seed is dependent on an encryption key set. Ifit is data scrambling without encryption, the initial value will befixed.

Since data stream attributes are transmitted over the auxiliary channel224, the main link packet headers serve as stream identification numbersthereby greatly reducing overhead and maximizing link bandwidth. Itshould also be noted that neither the main link 222 nor the auxiliarylink 224 has separate clock signal lines. In this way, the receivers onmain link 222 and auxiliary link 224 sample the data and extract theclock from the incoming data stream. Fast phase locking for any phaselock loop (PLLs) circuit in the receiver electrical sub layer isimportant for since the auxiliary channel 224 is half-duplexbi-directional and the direction of the traffic changes frequently.Accordingly, the PLL on the auxiliary channel receiver phase locks in asfew as 16 data periods thanks to the frequent and uniform signaltransitions of Manchester II (MII) code

At link set up time, the data rate of main link 222 is negotiated usingthe handshake over auxiliary channel 224. During this process, knownsets of training packets are sent over the main link 222 at the highestlink speed. Success or failure is communicated back to the transmitter102 via the auxiliary channel 224. If the training fails, main linkspeed is reduced and training is repeated until successful. In this way,the source physical layer 1102 is made more resistant to cable problemsand therefore more suitable for external host to monitor applications.However, unlike conventional display interfaces, the main channel linkdata rate is decoupled from the pixel clock rate. A link data rate isset so that link bandwidth exceeds the aggregate bandwidth of thetransmitted streams.

Source Device Link Layer

The source link layer 1204 handles the link initialization andmanagement. For example, upon receiving a hot plug detect eventgenerated upon monitor power-up or connection of the monitor cable fromthe source physical layer 1202, the source device link layer 1204evaluates the capabilities of the receiver via interchange over theauxiliary channel 224 to determine a maximum main link data rate asdetermined by a training session, the number of time-base recovery unitson the receiver, available buffer size on both ends, availability of USBextensions and then notifies the stream source 1206 of an associated hotplug event. In addition, upon request from the stream source 1206, thesource link layer 1204 reads the display capability (EDID orequivalent). During a normal operation, the source link layer 1204 sendsthe stream attributes to the receiver 104 via the auxiliary channel 224,notifies the stream source 1204 whether the main link 222 has enoughresource for handling the requested data streams, notifies the streamsource 1204 of link failure events such as sync loss and bufferoverflow, and sends MCCS commands submitted by the stream source 1204 tothe receiver via the auxiliary channel 224. All communications betweenthe source link layer 1204 and the stream source/sink use the formatsdefined in the application profile layer 1214.

Application Profile Layer (Source and Sink)

In general, the Application Profile Layer defines formats with which astream source (or sink) will interface with the associated link layer.The formats defined by the application profile layer are divided intothe following categories, Application independent formats (Link Messagefor Link Status inquiry) and Application dependent formats (main linkdata mapping, time-base recovery equation for the receiver, and sinkcapability/stream attribute messages sub-packet formats, if applicable).The Application Profile Layer supports the following color formats24-bit RGB, 16-bit RG2565, 18-bit RGB, 30-bit RGB, 256-color RGB (CLUTbased), 16-bit, CbCr422, 20-bit YCbCr422, and 24-bit YCbCr444.

For example, the display device application profile layer (APL) 1214 isessentially an application-programming interface (API) describing theformat for Stream Source/Sink communication over the main link 222 thatincludes a presentation format for data sent to or received from theinterface 100. Since some aspects of the APL 1214 (such as the powermanagement command format) are baseline monitor functions, they arecommon to all uses of the interface 100. Whereas other non-baselinemonitor functions, such as such as data mapping format and streamattribute format, are unique to an application or a type of isochronousstream that is to be transmitted. Regardless of the application, thestream source 1204 queries the source link layer 1214 to ascertainwhether the main link 222 is capable of handling the pending datastream(s) prior to the start any packet stream transmission on the mainlink 222.

When it is determined that the main link 222 is capable of supportingthe pending packet stream(s), the stream source 1206 sends streamattributes to the source link layer 1214 that is then transmitted to thereceiver over the auxiliary channel 224. These attributes are theinformation used by the receiver to identify the packets of a particularstream, to recover the original data from the stream and to format itback to the stream's native data rate. The attributes of the data streamare application dependent.

In those cases where the desired bandwidth is not available on the mainlink 222, the stream source 1214 may take corrective action by, forexample, reducing the image refresh rate or color depth.

Display Device Physical Layer

The display device physical layer 1216 isolates the display device linklayer 1210 and the display device APL 1216 from the signaling technologyused for link data transmission/reception. The main link 222 and theauxiliary channel 224 have their own physical layers, each consisting ofa logical sub layer and an electrical sub layer that includes theconnector specification. For example, the half-duplex, bi-directionalauxiliary channel 224 has both a transmitter and a receiver at each endof the link as shown in FIG. 15. An auxiliary link transmitter 1502 isprovided with link characters by a logical sub layer 1208-1 that arethen serialized serialized and transmitted to a corresponding auxiliarylink receiver 1504. The receiver 1504, in turn, receives serialized linkcharacter from the auxiliary link 224 and de-serializes the data at alink character clock rate. It should be noted that the major functionsof the source logical sub layers include signal encoding, packetizing,data scrambling (for EMI reduction), and training pattern generation forthe transmitter port. While for the receiver port, the major functionsof the receiver logical sub layer includes signal decoding,de-packetizing, data de-scrambling, and time-base recovery.

Auxiliary Channel

The major functions of auxiliary channel logical sub layer include dataencoding and decoding, framing/de-framing of data and there are twooptions in auxiliary channel protocol: standalone protocol (limited tolink setup/management functions in a point-to-point topology) is alightweight protocol that can be managed by the Link Layer state-machineor firmware and extended protocol that supports other data types such asUSB traffic and topologies such as daisy-chained sink devices. It shouldbe noted that the data encoding and decoding scheme is identicalregardless of the protocol whereas framing of data differs between thetwo.

Still referring to FIG. 15, the auxiliary channel electrical sub layercontains the transmitter 1502 and the receiver 1504. The transmitter1502 is provided with link characters by the logical sub layer, which itserializes and transmits out. The receiver 1504 receives serialized linkcharacter from the link layer and subsequently de-serializes it at linkcharacter clock rate. The positive and negative signals of auxiliarychannel 224 are terminated to ground via 50-ohm termination resistors ateach end of the link as shown. In the described implementation, thedrive current is programmable depending on the link condition and rangesfrom approximately 8 mA to approximately 24 mA resulting in a range ofVdifferential_pp of approximately 400 mV to approximately 1.2V. Inelectrical idle modes, neither the positive nor the negative signal isdriven. When starting transmission from the electrical idle state, theSYNC pattern must be transmitted and the link reestablished. In thedescribed embodiment, the SYNC pattern consists of toggling a auxiliarychannel differential pair signals at clock rate 28 times followed byfour 1's in Manchester II code. The auxiliary channel master in thesource device detects hot-plug and hot-unplug events by periodicallydriving or measuring the positive and negative signals of auxiliarychannel 224.

Main Link

In the described embodiment, the main link 222 supports discrete,variable link rates that are integer multiples of the local crystalfrequency (see FIG. 3 for a representative set of link rates consonantwith a local crystal frequency of 24-MHz). As shown in FIG. 16, the mainlink 222 (being an unidirectional channel) has only a transmitter 1602at the source device and only a receiver 1604 at the display device.

As shown, the cable 1604 takes the form includes a set of twisted pairwires, one for each of the Red (R), Green(G), and Blue(B) video signalsprovides in a typical RGB color based video system (such as PAL based TVsystems). As known by those of skill in the art, twisted pair cable is atype of cable that consists of two independently insulated wires twistedaround one another. One wire carries the signal while the other wire isgrounded and absorbs signal interference. It should be noted that insome other systems, the signals could also be component based signals(Pb, Pr, Y) used for NTSC video TV systems. Within the cable, eachtwisted pair is individually shielded. Two pins for +12V power andground are provided. The characteristics impedance of each differentialpair is 100 ohms+/−20%. The entire cable is also shielded. This outershield and individual shields are shorted to the connector shells onboth ends. The connector shells are shorted to ground in a sourcedevice. A connector 1700 as shown in FIG. 17 has 13 pins in one rowhaving a pinout that is identical both for the connector on the sourcedevice end and that on the display device end. The source devicesupplies the power.

The main link 222 is terminated on both ends and since the main link 222is AC coupled, the termination voltage can be anywhere between 0V(ground) to +3.6V. In the described implementation, the drive current isprogrammable depending on the link condition and ranges fromapproximately 8 mA to approximately 24 mA resulting in a range ofVdifferential_pp of approximately 400 mV to approximately 1.2V. Theminimum voltage swing is selected for each connection using a trainingpattern. An electrical idle state is provided for power managementmodes. In electrical idle, neither the positive nor the negative signalsare driven. When starting a transmission from electrical idle state, thetransmitter must conduct a training session in order re-establish thelink with the receiver.

State Diagrams

The invention will now be described in terms of state diagrams shown inFIGS. 18 and 19 described below. Accordingly, FIG. 18 shows the sourcestate diagram described below. At an off state 1802, the system is offsuch that the source is disabled. If the source is enabled, then thesystem transitions to a standby state 1804 suitable for power saving andreceiver detection. In order to detect whether or not the receiver ispresent (i.e., hot plug/play), the auxiliary channel is periodicallypulsed (such as for 1 us every 10 ms) and a measure of a voltage dropacross the termination resistors during the driving is measured. If itis determined that a receiver is present based upon the measured voltagedrop, then the system transitions to a detected receiver state 1806indicating that a receiver has been detected, i.e., a hot plug event hasbeen detected. If, however, there is no receiver detected, then thereceiver detection is continued until such time, if ever, a receiver isdetected or a timeout has elapsed. It should be noted that in some casesthe source device may choose to go to “OFF” state from which no furtherdisplay detection is attempted.

If at the state 1806 a display hot unplug event is detected, then thesystem transitions back to the standby state 1804. Otherwise the sourcedrives the auxiliary channel with a positive and negative signal to wakeup receiver and the receiver's subsequent response, if any, is checked.If there is no response received, then the receiver has not woken up andsource remains in the state 1806. If, however, a signal is received fromthe display, then the display has woken up and the source is ready readthe receiver link capabilities (such as max link rate, buffer size, andnumber of time-base recovery units) and the system transitions to a mainlink initialization state 1808 and is ready to commence a training startnotification phase.

At this point, a training session is started by sending a trainingpattern over the main link at a set link rate and checks an associatedtraining status. The receiver sets a pass/fail bit for each of threephases and the transmitter will proceed to the next phase upon detectionof pass only such that when a pass is detected, the main link is readyat that link rate. At this point, the interface transitions to a normaloperation state 1510, otherwise, the link rate is reduced and thetraining session is repeated. During the normal operation state 1810,the source continues to periodically monitor a link status index, whichif fails, a hot unplug event is detected and the system transitions tothe standby state 1804 and waits for a hot plug detection event. If,however, a sync loss is detected, then the system transitions to state1808 for a main link re-initiation event.

FIG. 19 shows the display state diagram 1900 described below. At a state1902, no voltage is detected, the display goes to an OFF state. At astandby mode state 1904, both main link receiver and auxiliary channelslave are in electrical idle, a voltage drop across the terminationresistors of auxiliary channel slave port are monitored for apredetermined voltage. If the voltage is detected, then the auxiliarychannel slave port is turned on indicating a hot plug event and thesystem moves to a display state 1906, otherwise, the display remains inthe standby state 1904. At the state 1906 (main link initializationphase), if a display is detected, then the auxiliary slave port is fullyturned on, and the transmitter responds to a receiver link capabilityread command and the display state transitions to 1908, otherwise, ifthere is no activity on the auxiliary channel for more than apredetermined period of time then the auxiliary channel slave port isput into the to standby state 1904.

During a training start notification phase, the display responds to thetraining initiation by the transmitter by adjusting the equalizer usingtraining patterns, updating the result for each phase. If the trainingfails, then wait for another training session and if the trainingpasses, then go to normal operation state 1910. If there is no activityon the auxiliary channel or on the main link (for training) for morethan a predetermined (10 ms, for example), the auxiliary channel slaveport is set to the standby state 1904.

FIGS. 20-24 show particular implementations of the cross platformdisplay interface.

FIG. 20 shows a PC motherboard 2000 having an on-board graphics engine2002 that incorporates a transmitter 2004 in accordance with theinvention. It should be noted that the transmitter 2004 is a particularexample of the transmitter 102 shown in FIG. 1. In the describedembodiment, the transmitter 2004 is coupled to an connector 2006 (alongthe lines of the connector 1700) mounted on the motherboard 2000 whichin turn is connected to a display device 2008 by way of a twisted paircable 2010 couples a display device 2010.

As known in the art, PCI Express (developed by Intel Corporation ofSanta Clara, Calif.) is a high-bandwidth, low pin count, serial,interconnect technology that also maintains software compatibility withexisting PCI infrastructure. In this configuration, the PCI Express portis augmented to become compliant with the requirements of the crossplatform interface which can directly drive a display device eitherusing a motherboard mounted connector as shown.

In situations where it is not practical to mount the connector on themotherboard, the signals can be routed through the SDVO slot of the PCIExpress motherboard and brought to the back of the PC using a passivecard connector as shown in FIG. 21. As is the case with the currentgeneration of add-in graphics cards, a add-in graphics card can supplantthe onboard graphics engine as shown in FIG. 23.

In the case of notebook applications, the transmitter on the motherboardgraphics engine would drive through internal cabling, an integratedreceiver/TCON which would drive the panel directly. For the most costeffective implementation, the receiver/TCON would be mounted on thepanel thereby reducing the number of interconnect wires to 8 or 10 asshown in FIG. 24

All of the above examples assume integrated transmitters. However, is itquite feasible to implement as a standalone transmitter integrating intoPCI and PCI Express environments through the AGP or SDVO slots,respectively. A standalone transmitter will enable output streamswithout any change in graphics hardware or software.

Flowchart Embodiments

The methodology of the invention will now be described in terms of anumber of flowcharts each describing a particular process for enablingthe invention. Specifically, FIGS. 25-29 describe a number ofinterrelated processes that when used singly or in any combinationdescribed aspects of the invention.

FIG. 25 shows a flowchart detailing a process 2500 for determining anoperational mode of the interface 100 in accordance with an embodimentof the invention. In this process, the operational mode will only be setto a digital mode if the video source and the display device are bothdigital. Otherwise, the operational mode will be set to analog mode. Itshould be noted that “analog mode” in this context can include bothconventional VGA mode as well as enhanced analog mode havingdifferential analog video with embedded alignment signal andbi-directional sideband. This enhanced analog mode will be describedbelow.

In step 2502, a video source is interrogated to determine whether thevideo source supports analog or digital data. If the video sourcesupports only analog data, the operational mode of coupling device 100will be set to analog (step 2508), then the process will end (step2512).

If the video source can output digital data, the process continues tostep 2506. The display device is then interrogated to determine whetherthe display device is configured to receive digital data. If the displaydevice supports only analog data, the operational mode of couplingdevice will be set to analog (step 2508), then the process will end(step 2512). Otherwise, the operational mode of the coupling device isset to digital (step 2510). For example, a processor may controlswitches within the coupling device to set the mode to digital. Ingeneral, the coupling device is configured to operate in a fully digitalmode only when both the video source and the video sink are operating ina corresponding digital mode.

FIG. 26 shows a flowchart detailing a process 2600 for providing a realtime video image quality check in accordance with some aspects of theinvention. In this example, all determinations of process 2600 are madeby a processor coupled to the display interface.

In step 2600, a video signal is received from a video source. Next, asignal quality test pattern is provided by the video source associatedwith the received video signal (step 2602). In step 2604, adetermination of a bit error rate is made, based upon the quality testpattern. Then, a determination is made of whether the bit error rate isgreater than a threshold value (step 2606). If the bit error rate isdetermined to not be greater than the threshold value, then adetermination is made (step 2614) of whether or not there are more videoframes. If it is determined that there are more video frames, then theprocess returns to step 2600. Otherwise, the process ends.

However, if the bit error rate is determined to be greater than thethreshold value in step 2606, a determination is made (step 2608) as towhether the bit rate is greater than a minimum bit rate. If the bit rateis greater than a minimum bit rate, then the bit rate is lowered (step2610) and the process returns to step 2606. If the bit rate is notgreater than the minimum bit rate, then the mode is changed to analogmode (step 2612) and the process ends.

FIG.27 a and 27 b show a flowchart for a link set up process 2700 inaccordance with an embodiment of the invention. The process 2700 beginsat 2702 by the receiving of a hot plug detection event notification. At2704 a main link inquiry is made by way of an associated auxiliarychannel to determine a maximum data rate, a number of time base recoveryunits included in a receiver, and available buffer size. Next, at 2706,the maximum link data rate is verified by way of a training session andat 2708, a data stream source is notified of the hot plug event. At2710, the capabilities of the display (using EDID, for example) aredetermined by way of the auxiliary channel and the display responds tothe inquires at 2712 which, in turn, results a collaboration of the mainlink training session at 2714.

Next, at 2716, the stream source sends stream attributes to the receiverby way of the auxiliary channel and at 2718, the stream sources arefurther notified whether the main link is capable of supporting therequested number of data streams at 2720. At 2722, the various datapackets are formed by adding associated packet headers and themultiplexing of a number of source streams is scheduled at 2724. At 2726a determination is made whether or not the link status is OK. When thelink status is not OK, then the source(s) are notified of a link failureevent at 2728, otherwise, the link data streams are reconstructed intothe native streams based upon the various packet headers at 2730. At2732, the reconstructed native data streams are then passed to thedisplay device.

FIG. 28 shows a flowchart detailing a process 2800 for performing atraining session in accordance with an embodiment of the invention. Itshould be noted that the training session process 2800 is oneimplementation of the operation 2506 described in FIG. 25. A trainingsession is started at 2802 by sending a training pattern over the mainlink at a set link rate to the receiver. A typical link training patternis shown in FIG. 11 in accordance with an embodiment of the invention.As illustrated, during the training session, a phase 1 represents theshortest run length while phase 2 is the longest. The receiver is to usethese two phases to optimize the equalizer. In phase 3, both bit lockand character lock are achieved as long as the link quality isreasonable. At 2804, the receiver checks an associated training statusand based upon the training status check, the receiver sets a pass/failbit for each of three phases and the transmitter at 2806. At each phase,the receiver will proceed to the next phase upon detection of pass onlyand at 2810 and if the receiver does not detect a pass then the receiverreduces the link rate and repeats the training session. The main link isready at that link rate at which a pass is detected at 2812.

FIG. 29 illustrates a computer system 2900 employed to implement theinvention. Computer system 2900 is only an example of a graphics systemin which the present invention can be implemented. Computer system 2900includes central processing unit (CPU) 1510, random access memory (RAM)2920, read only memory (ROM) 2925, one or more peripherals 2930,graphics controller 2960, primary storage devices 2940 and 2950, anddigital display unit 2970. As is well known in the art, ROM acts totransfer data and instructions uni-directionally to the CPUs 2910, whileRAM is used typically to transfer data and instructions in abi-directional manner. CPUs 2910 may generally include any number ofprocessors. Both primary storage devices 2940 and 2950 may include anysuitable computer-readable media. A secondary storage medium 880, whichis typically a mass memory device, is also coupled bi-directionally toCPUs 2910 and provides additional data storage capacity. The mass memorydevice 880 is a computer-readable medium that may be used to storeprograms including computer code, data, and the like. Typically, massmemory device 880 is a storage medium such as a hard disk or a tapewhich generally slower than primary storage devices 2940, 2950. Massmemory storage device 880 may take the form of a magnetic or paper tapereader or some other well-known device. It will be appreciated that theinformation retained within the mass memory device 880, may, inappropriate cases, be incorporated in standard fashion as part of RAM2920 as virtual memory.

CPUs 2910 are also coupled to one or more input/output devices 890 thatmay include, but are not limited to, devices such as video monitors,track balls, mice, keyboards, microphones, touch-sensitive displays,transducer card readers, magnetic or paper tape readers, tablets,styluses, voice or handwriting recognizers, or other well-known inputdevices such as, of course, other computers. Finally, CPUs 2910optionally may be coupled to a computer or telecommunications network,e.g., an Internet network or an intranet network, using a networkconnection as shown generally at 2995. With such a network connection,it is contemplated that the CPUs 2910 might receive information from thenetwork, or might output information to the network in the course ofperforming the above-described method steps. Such information, which isoften represented as a sequence of instructions to be executed usingCPUs 2910, may be received from and outputted to the network, forexample, in the form of a computer data signal embodied in a carrierwave. The above-described devices and materials will be familiar tothose of skill in the computer hardware and software arts.

Graphics controller 2960 generates analog image data and a correspondingreference signal, and provides both to digital display unit 2970. Theanalog image data can be generated, for example, based on pixel datareceived from CPU 2910 or from an external encode (not shown). In oneembodiment, the analog image data is provided in RGB format and thereference signal includes the VSYNC and HSYNC signals well known in theart. However, it should be understood that the present invention can beimplemented with analog image, data and/or reference signals in otherformats. For example, analog image data can include video signal dataalso with a corresponding time reference signal.

Although only a few embodiments of the present invention have beendescribed, it should be understood that the present invention may beembodied in many other specific forms without departing from the spiritor the scope of the present invention. The present examples are to beconsidered as illustrative and not restrictive, and the invention is notto be limited to the details given herein, but may be modified withinthe scope of the appended claims along with their full scope ofequivalents.

While this invention has been described in terms of a preferredembodiment, there are alterations, permutations, and equivalents thatfall within the scope of this invention. It should also be noted thatthere are many alternative ways of implementing both the process andapparatus of the present invention. It is therefore intended that theinvention be interpreted as including all such alterations,permutations, and equivalents as fall within the true spirit and scopeof the present invention.

Minimizing buffer requirements, in a packet based multimedia systemhaving a multimedia source device coupled to a multimedia display deviceby way of a bi-directional auxiliary channel arranged to transferinformation between the display device and the source device and viceversa and a unidirectional main link arranged to carry multimedia datapackets from the multimedia source device to the multimedia displaydevice by interspersing special characters that allow the display deviceto distinguish each bit of pixel data included in the data packetsthereby requiring only a small FIFO type buffer unit.

1. In a digital packet based multimedia system having a multimediasource device coupled to a multimedia display device by way ofbi-directional auxiliary channel line arranged to transfer informationbetween the display device and a source device and vice versa and aunidirectional main link line arranged to carry multimedia data packetsin the form of an multimedia data packet stream from the multimediasource device to the multimedia display device wherein each of themultimedia data packets includes at least a multimedia data packetheader, wherein the main link line is physically separate from theauxiliary channel line, a method of reducing multimedia packet overhead,comprising: prior to commencement of transmission of the data packetsfrom the source device to the display device over the main link line,communicating via the auxiliary channel line multi-media data packetstream attributes to the display device, wherein the data packet streamattributes include information used by the display device to at leastidentify the data packets of a particular stream, to recover originaldata from the multimedia data packet stream and to format the multimediadata packet stream back to a data packet stream native data rate;replacing the data packet header with a corresponding reduced size datapacket header for each of the multimedia data packets at the sourcedevice commensurate with the data packet stream attributes alreadycommunicated via the auxiliary channel line; streaming the multi-mediadata packets having the reduced size data packet header from the sourcedevice to the display device; and sending information associated withthe streaming between the source device and the display device by way ofthe auxiliary channel line concurrent with the streaming, wherein thereis no clock line.
 2. A method as recited in claim 1, wherein a datapacket is one of a number of associated multimedia data packets thattaken together form multimedia data packet stream.
 3. A method asrecited in claim 1, wherein the multimedia data packet stream is one ofa number of multimedia data packet streams each having an associatedadjustable data stream link rate that is independent of a native streamrate.
 4. A method as recited in claim 1, further comprising: forming anumber of virtual links each being associated with a particular one of aplurality of multi media data packet streams wherein each of saidvirtual links has an associated virtual link bandwidth and a virtuallink rate.
 5. A method as recited in claim 4, wherein a main link linebandwidth is at least equal to an aggregate of the associated virtuallink bandwidths.
 6. In a digital packet based multimedia system having amultimedia source device coupled to a multimedia display device by wayof a bi-directional auxiliary channel line arranged to transferinformation between the display device and a source device and viceversa and a unidirectional main link line arranged to carry multimediadata packets in the form of an multimedia data packet stream from themultimedia source device to the multimedia display device wherein eachof the multimedia data packets includes at least a multimedia datapacket header, wherein the main link line is physically separate fromthe auxiliary channel line, an apparatus for reducing multimedia packetoverhead, comprising: means for communicating via the auxiliary channelline multi-media data packet stream attributes to the display deviceprior to commencement of transmission of the data packets from thesource device to the display device over the main link line, wherein thedata packet stream attributes include information used by the displaydevice to at least identify the data packets of a particular stream, torecover original data from the multimedia data packet stream or toformat the multimedia data packet stream back to a data packet streamnative data rate; means for replacing the data packet header with acorresponding reduced size data packet header for each of the multimediadata packets at the source device commensurate with the data packetstream attributes already communicated via the auxiliary channel line;means for streaming the multi-media data packets having the reduced sizedata packet header from the source device to the display deviceconcurrently; and means for sending information associated with thestreaming between the source device and the display by way of theauxiliary channel line concurrent with the streaming, wherein there isno clock line.
 7. An apparatus as recited in claim 6, wherein a datapacket is one of a number of associated multimedia data packets thattaken together form the multimedia data packet stream.
 8. An apparatusas recited in claim 7, wherein the multimedia data packet stream is oneof a number of multimedia data packet streams each having an associatedadjustable data stream link rate that is independent of a native streamrate.
 9. An apparatus as recited in claim 7, further comprising: meansfor forming a number of virtual links each being associated with aparticular one of the multi media data packet streams wherein each ofsaid virtual links has an associated virtual link bandwidth and avirtual link rate.
 10. An apparatus as recited in claim 9, wherein amain link line bandwidth is at least equal to an aggregate of theassociated virtual link bandwidths.
 11. Computer readable medium encodedwith a computer program and executable by a processor for reducingmultimedia packet overhead in a digital packet based multimedia systemhaving a multimedia source device coupled to a multimedia display deviceby way of a bi-directional auxiliary channel line arranged to transferinformation between the display device and a source device and viceversa and a unidirectional main link line arranged to carry multimediadata packets in the form of an multimedia data packet stream from themultimedia source device to the multimedia display device wherein eachof the multimedia data packets includes at least a multimedia datapacket header, wherein the main link line is physically separate fromthe auxiliary channel line, comprising: computer code for communicatingvia the auxiliary channel line multi-media data packet stream attributesto the display device prior to commencement of transmission of the datapackets from the source device to the display device over the main linkline, wherein the data packet stream attributes include information usedby the display device to at least identify the data packets of aparticular stream, to recover original data from the multimedia datapacket stream or to format the multimedia data packet stream back to adata packet stream native data rate; computer code for replacing thedata packet header with a corresponding reduced size data packet headerfor each of the multimedia data packets at the source devicecommensurate with the data packet stream attributes already communicatedvia the auxiliary channel line; and computer code for streaming themulti-media data packets having the reduced size data packet header fromthe source device to the display device; computer code for sendinginformation associated with the streaming between the source device andthe display by way of the auxiliary channel line concurrent with thestreaming; and computer readable medium for storing the computer code.12. Computer readable medium as recited in claim 11, wherein a datapacket is one of a number of associated multimedia data packets thattaken together form the multimedia data packet stream.
 13. Computerreadable medium as recited in claim 11, wherein the multimedia datapacket stream is one of a number of multimedia data packet streams eachhaving an associated adjustable data stream link rate that isindependent of a native stream rate.
 14. Computer readable medium asrecited in claim 11, further comprising: forming a number of virtuallinks each being associated with a particular one of a plurality ofmulti media data packet streams wherein each of said virtual links hasan associated virtual link bandwidth and a virtual link rate. 15.Computer readable medium as recited in claim 14, wherein a main linkline bandwidth is at least equal to an aggregate of the associatedvirtual link bandwidths.
 16. A computer chip configured to perform amethod in a digital packet based multimedia system having a multimediasource device coupled to a multimedia display device by way of abi-directional auxiliary channel line arranged to transfer informationbetween the display device and a source device and vice versa and aunidirectional main link line arranged to carry multimedia source datapackets in the form of an multimedia data packet stream from themultimedia source device to the multimedia display device wherein eachof the multimedia data packets includes at least a multimedia datapacket header, wherein the main link line is physically separate fromthe auxiliary channel line, a method of reducing multimedia packetoverhead, the method comprising: prior to commencement of transmissionof the data packets from the source device to the display device overthe main link line, communicating via the auxiliary channel linemulti-media data packet stream attributes to the display device, whereinthe data packet stream attributes include information used by thedisplay device to at least identify the data packets of a particularstream, to recover original data from the multimedia data packet streamand to format the multimedia data packet stream back to a data packetstream native data rate; replacing the data packet header with acorresponding reduced size data packet header for each of the multimediadata packets at the source device commensurate with the data packetstream attributes already communicated via the auxiliary channel line;streaming the multi-media data packets having the reduced size datapacket header from the source device to the display device; and sendinginformation associated with the streaming between the source device andthe display device by way of the auxiliary channel line concurrent withthe streaming, wherein there is no clock line.
 17. In a digital packetbased multimedia system having a multimedia source device coupled to amultimedia display device by way of a bi-directional auxiliary channelline arranged to transfer information between the display device and asource device and vice versa and a unidirectional main link linearranged to carry multimedia data packets in the form of an multimediadata packet stream from the multimedia source device to the multimediadisplay device wherein each of the multimedia data packets includes atleast a multimedia data packet header, wherein the main link line isphysically separate from the auxiliary channel line, a method ofreducing multimedia packet overhead, comprising: prior to commencementof transmission of the data packets from the source device to thedisplay device over the main link line, receiving via the auxiliarychannel multi-media data packet stream attributes from the multimediasource device, wherein the data packet stream attributes includeinformation used by the display device to at least identify the datapackets of a particular stream, to recover original data from the datapacket stream and to form the data packet stream back to a data packetstream native data rate; replacing the data packet header with acorresponding reduced size data packet header for each of the multimediadata packets at the source device commensurate with the data packetstream attributes already communicated via the auxiliary channel line;receiving a stream of multimedia data packets having a data packetheader with a size that was reduced by the multimedia source device byreplacing the data packet header with a corresponding reduced size datapacket header for each of the multimedia data packets at the sourcedevice commensurate with the data packet stream attributes alreadycommunicated via the auxiliary channel line; and receiving informationassociated with the streaming by way of the auxiliary channel lineconcurrent with the receiving of the stream of multimedia data packets,wherein there is no clock line.